Phthalic anhydride (P.A.) is the cornerstone of Stepan’s vertically integrated Polymers division. The phthalic anhydride plant is an integral part of the ISO 9001:2008 Stepan Millsdale site, located in Elwood, Illinois. P.A. is manufactured at this site to supply the internal requirements of the STEPANPOL® polyester polyols product line. In addition, Stepan is a major P.A. supplier to the North American merchant market.